The goal of the proposed research is to develop methods for storage of platelets at 22 degrees centigrade so that after three days there is negligible difference in their viability and function when compared to fresh platelets. Optimal concentrate volume, container type, method of agitation, and external gas tension will be determined empirically. Storage beyond 72 hours will then be explored. Studies of biochemical and physiologic events occurring during storage will be carried out with emphasis on adenine nucleotide metabolism, energy substrate metabolism, lipid metabolism, membrane glycoproteins, and plasma coagulant proteins. The mechanisms by which platelets might be injured by the centrifugation process necessary to concentrate them will be explored. Results of in vitro studies such as platelet aggregation and shape change, osmotic reversal, Coulter counter size distribution before and after ADP addition, and oil phase microscopy will be correlated with in vivo studies of the survival of 51-chromium labeled platelets in normal volunteers and measurements of bleeding time in thrombocytopenic recipients of stored platelets.